The present invention relates to a carburetor arrangement for a manually guided implement, especially a brushcutter, a chain saw, or the like, that is operated by an internal combustion engine.
With an implement having an internal combustion engine for a drive motor, a carburetor is provided that supplies a fuel/air mixture to the internal combustion engine. For an optimum engine performance, and to fulfill emission regulations, the carburetor is set for warm engine operation. A butterfly valve that is pivotably mounted in the intake duct of the carburetor serves for controlling the power. The pivot range extends from the fully opened state for full throttle operation to a nearly completely closed state in which the internal combustion engine is idling.
The basic setting of the carburetor is suitable for the start of the internal combustion engine only to a limited extent. When starting a cold internal combustion engine, an enrichment of the fuel/air mixture is necessary, for which a starter valve, also known as a choke valve, is provided upstream of the butterfly valve. When the choke valve is closed at least partially, the underpressure in the carburetor, and hence the quantity of fuel drawn in, increase, thereby bringing about the desired enrichment. For a reliable start, at the same time a position of the butterfly valve is necessary that is open by an additional amount relative to the idling position. For a warm start, a similar position of the butterfly valve can be expedient, whereby a closing of the choke valve is not necessary. Depending upon the various operating conditions, different relative settings of the butterfly valve and of the choke valve are necessary for the start of the internal combustion engine.
An unintentional actuation of a start lever that acts upon the choke valve can lead to increased exhaust gas emissions. Incorrect settings of the valve arrangement can also make starting difficult. The butterfly valve, when opened beyond the idling position, after start-up generates an increased initial speed, which is disadvantageous when using a centrifugal clutch.
It is an object of the present application to improve the carburetor arrangement of the aforementioned type for a manually-guided implement that is operated by an internal combustion engine such that a reliable start is achieved.